1. Field of the Invention
The present invention relates to a production method of an optical fiber preform and a production method of an optical fiber.
2. Description of the Related Art
A multi-core fiber (MCF) is an optical fiber including a plurality of cores in one optical fiber, and is new type of optical fiber capable of disposing many core portions in a reduced space. This multi-core fiber makes us anticipate realization of new optical propagation such as large-capacity transmission of image and spatial multiplexing transmission or the like.
A production method of a multi-core fiber includes, for example, a stack-and-draw method, a drilling method or the like.
The stack-and-draw method is used to form an optical fiber preform by disposing glass rods for forming a cladding of which refractive index is lower than that of the cores around glass rods (core preforms) for forming the cores, inserting them into a jacket tube made of glass, and then heating and drawing them (for example, see Japanese Patent Application Laid-open Publication No. H8-119656).
The drilling method is used to form an optical fiber preform by forming holes (through holes) in a rod-shaped base material made of glass with a drill, and inserting glass rods (core preforms) for forming cores into the holes (for example, see Japanese Patent Application Laid-open Publication No. H9-90143).
However, the stack-and-draw method had a problem that a positioning accuracy for the core decreased since the core preforms are inserted inside the jacket tube to be subjected to heating and drawing. Also, the drilling method had a problem of increased machining cost since the holes are formed on the rod-shaped base material with the drill.
To address this, Japanese Patent Application Laid-open Publication No. S57-82805 discloses a production method of a multi-core fiber preform for obtaining the multi-core fiber preform by arranging a plurality of core preforms for forming cores at predetermined positions, depositing glass particles from outside these core preforms, forming a porous layer becoming a cladding, and then sintering it.